Forum: Ruby how to find and close opened file descriptor

Announcement (2017-05-07): www.ruby-forum.com is now read-only since I unfortunately do not have the time to support and maintain the forum any more. Please see rubyonrails.org/community and ruby-lang.org/en/community for other Rails- und Ruby-related community platforms.
Oliver P. (Guest)
on 2009-05-07 19:54
During my testing, I found that ruby doesn't create IO object for each
opened file descriptor which are inherited from parent process. So we
have to close all these opened file descriptor except stdin, stdout and
stderr by following way:

     3.upto(1023) do |fd|
        begin
          if io = IO::new(fd)
            io.close
          end
        rescue
        end
      end

But I really don't like this way. Is there better way that I can find
all opened file descriptors.

And now I am assuming the maximum file no is 1023. Is there any way that
I can get the maximum file no?

Thanks.
Roger P. (Guest)
on 2009-05-08 16:50
> And now I am assuming the maximum file no is 1023. Is there any way that
> I can get the maximum file no?

You could run a loop at the beginning of your script which detects it :)

count = 0
all = []
begin
 loop { all << File.open('test','w') }
rescue Exception
 count = all.length
 for file in all do; file.close; end
end
count

But getting back to your original question, another way to close
descriptors is
GC.each_object(IO) do |io| io.close; end

I guess.  Not totally sure what you mean by "doesnt create file
descriptors for each inherited object" ?
Thanks.
-=r
Oliver P. (Guest)
on 2009-05-08 17:55
Roger P. wrote:
>> And now I am assuming the maximum file no is 1023. Is there any way that
>> I can get the maximum file no?
>
> You could run a loop at the beginning of your script which detects it :)
>
> count = 0
> all = []
> begin
>  loop { all << File.open('test','w') }
> rescue Exception
>  count = all.length
>  for file in all do; file.close; end
> end
> count
>
> But getting back to your original question, another way to close
> descriptors is
> GC.each_object(IO) do |io| io.close; end
>
> I guess.  Not totally sure what you mean by "doesnt create file
> descriptors for each inherited object" ?
> Thanks.
> -=r

At first, I also try to find all IO objects and close. Here is the code:

ObjectSpace.each_object(IO) do |io|
    begin
      unless io.closed?
        io.close
      end
    rescue ::Exception
    end
end

But it doesn't work because ruby doesn't create IO object for the open
file descriptor which are inherited from parent process.
Eleanor McHugh (Guest)
on 2009-05-08 18:58
(Received via mailing list)
On 8 May 2009, at 14:55, Oliver P. wrote:
> end
>
> But it doesn't work because ruby doesn't create IO object for the open
> file descriptor which are inherited from parent process.

You should probably describe how your parent process is opening these
file descriptors as clearly it's not via objects in the IO hierarchy
or they would be accessible in the child process. As a general rule
though, if you have control over where and when the file descriptors
are coming into play you can use the IO.for_fd(file_descriptor) method
and store them in a *shudder* global variable or constant...

  OPEN_FILES = []
  ...
  ...
  fd = some_method_that_opens_file_and_returns_descriptor
  OPEN_FILES << IO.for_fd(fd)
  ...
  ...

Then in the spawned child process closing these would be as simple as:

  OPEN_FILES.each { |file| file.close }



Ellie

Eleanor McHugh
Games With Brains
http://slides.games-with-brains.net
----
raise ArgumentError unless @reality.responds_to? :reason
Gary W. (Guest)
on 2009-05-08 19:32
(Received via mailing list)
On May 7, 2009, at 11:54 AM, Oliver P. wrote:

>          end
>        rescue
>        end
>      end
>
> But I really don't like this way. Is there better way that I can find
> all opened file descriptors.

I believe this is the standard idiom on *nix type systems to close all
file descriptors when you have no particular knowledge of which ones
are open.

In other words there is no standard way to ask the OS for a list of
open descriptors via a simple system call.

A possible alternative is to parse the output of utilities like 'lsof'
to determine what file descriptors are open or to dig into the various
platform specific ways that those utilities query the kernel for this
information.

Gary W.
Roger P. (Guest)
on 2009-05-08 19:49
> I believe this is the standard idiom on *nix type systems to close all
> file descriptors when you have no particular knowledge of which ones
> are open.

I think that's right except for maybe solaris has a helper or something,
but there's no standard.
-=r
Daniel B. (Guest)
on 2009-05-08 20:02
(Received via mailing list)
On May 7, 9:54 am, Oliver P. <removed_email_address@domain.invalid> wrote:
>         rescue
>         end
>       end
>
> But I really don't like this way. Is there better way that I can find
> all opened file descriptors.
>
> And now I am assuming the maximum file no is 1023. Is there any way that
> I can get the maximum file no?

The io-extra library might be able to help you, depending on your
platform.

gem install io-extra.

Take a look at the IO.closefrom and IO.fdwalk methods.

Regards,

Dan
This topic is locked and can not be replied to.